1. Field of the Invention
The present invention relates to a photochemical process for grafting haloolefins onto polyamide substrates and to products produced thereby.
2. Brief Description of the Prior Art
In space exploration, extravehicular activity (EVA) is essential. Such activity necessarily requires the use of high strength fibrous materials from which to fabricate garments, carrying bags and the like used in such activity. In addition to having the necessary physical properties, the materials employed must be flame resistant in high oxygen atmospheres. In space vehicles, it is common to encounter highly oxygen enriched atmospheres. This is also true of deep sea diving vessels. Thus, for example, while many synthetic polymeric materials possess suitable mechanical and physical properties which make them ideally suited for the manufacture of fabrics useful in space and deep sea exploration, they suffer from the infirmity that they are not sufficiently flame retardant and indeed, in many cases, are highly flammable in such oxygen enriched environments.
The fiber forming aromatic polyamides such as poly (m-phenyleneisophthalamide) are ideally suited in many respects for fabrics used in space travel and deep sea exploration. However, these materials are not flame resistant in highly enriched oxygen atmospheres, i.e. oxygen contents of around 30% by volume. Heretofore, it has been proposed to improve the flame resistance of such materials through chemical modification by phosphorylation and halogenation. However, such treatments strongly color the fibers and also degrade the aromatic polyamide thereby reducing many of its mechanical properties.
It is known that unsaturated monomeric materials can be grafted to polymeric substrates using various irradiation techniques. Examples of such processes can be found in U.S. Pat. Nos. 2,956,899 to Cline, 3,412,175 to Magat et al, and 3,933,607 to Needles et al. The process of the Cline patent involves irradiating polymeric substrates in the presence of a controlled amount of oxygen followed by contacting the activated substrate with a liquid polymerizable monomer. The Magat et al patent discloses a grafting technique in which the polymeric substrate is contacted with a fluorinated monomer in the presence of high energy radiation. The Magat process like the Cline process suffers from the infirmity that the polymeric substrate must be soaked in the liquid monomer or a solution thereof. The Needles et al patent discloses the vapor phase photografting of monomers onto polymeric substrates but requires a two-step process in which the substrate is first treated with a wetting agent following which the substrate is contacted with a photosensitizer and the monomer in the presence of a radiation source.